Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.67   3.484%   $56.5747   $56.57   $56.55   $56.60  
  Purchase #2 $133.70   8.692%   $145.3212   $145.32   $145.30   $145.30  
  Purchase #3 $50.60   6.829%   $54.0555   $54.06   $54.05   $54.10  
  Purchase #4 $89.66   3.504%   $92.8017   $92.80   $92.80   $92.80  
  Purchase #5 $117.32   7.794%   $126.4639   $126.46   $126.45   $126.50  
  Purchase #6 $156.29   9.267%   $170.7734   $170.77   $170.75   $170.80  
  Purchase #7 $105.98   10.577%   $117.1895   $117.19   $117.20   $117.20  
  7 purchase totals = $708.22       $763.1799   $763.17   $763.10   $763.30